A theoretical study of nickel at high temperatures and high pressures suggests that the metal could play a crucial role in generating the Earth’s magnetic field. That’s the conclusion of Giorgio Sangiovanni of the University of Würzburg and an international team, which has done calculations suggesting that the thermal conductivity of nickel is much lower than that of iron under these extreme conditions.
The geodynamo model says that the Earth’s magnetic field is created by the flow of liquid iron in the outer core of the Earth. This flow is driven by the convection of heat from the inner core to the mantle. A problem with this model is that the thermal conductivity of iron is predicted to be very high at the relevant pressures and temperatures – and this means that convection should not occur.
Crystal structure
Compared to some other metals, iron and nickel are relatively poor thermal conductors under ambient conditions. At high pressures and temperatures, however, the crystal structure of iron is expected to change – resulting in a large increase in its thermal conductivity. By performing calculations at Germany’s Leibniz Supercomputing Centre, Sangiovanni and colleagues have shown that nickel is likely to retain its crystal structure – and poor thermal conductivity – at high pressures and temperatures.
Writing in Nature Communications, the team suggests that further research is needed into the possible contributions of nickel and iron/nickel alloys to the convection that is believed to be driving the Earth’s magnetic field.
Get me out of here: Plato’s book The Republic tells of Socrates likening the process of education to an escape from a cave. (Painted by Mattia Preti 1649)
I never fully realized the perilous state of the humanities until I read recent remarks by physicists about “Plato’s cave”, one of the oldest and most influential allegories in Western literature. It appears in Plato’s book The Republic, which was written in about 380 BC. In the book, Plato recounts an extended conversation between his teacher, Socrates, and a group of Athenian youths on the nature of justice. Socrates regards education as vital to justice, and at the thematic core of The Republic likens the process of education to an escape from a cave.
Several physicists have recently given their own take on the meaning of this allegory. The Italian physicist Carlo Rovelli mentions it at the beginning of Reality Is Not What It Seems (Penguin 2016), describing scientific thinking – or the fashioning of “novel and more effective images of the world” – as the right way to escape the cave. Meanwhile, in The Greatest Story Ever Told – So Far: Why Are We Here? (Simon and Schuster 2017), US cosmologist Lawrence Krauss says that “Plato’s vision of ‘pure thought’ has been replaced by the scientific method”, which uncovers “the underlying realities of the world”.
So what’s the harm in stretching one’s interpretation of a book written almost 2500 years ago? A lot.
Not what it seems
The allegory – as told originally in The Republic – unfolds as follows. Imagine a cave, Socrates asks his companions, in which a community of people are chained in place so they face a wall, and are captivated by the images they see on it. The process of education unfolds in three steps.
In step one, individuals break free of the bonds and are able to turn around and see that the images are just shadows cast by other objects that a cohort of people are moving back and forth in front of a fire. Today’s teachers often compare that situation to a cinema, in which members of the audience, who have spent their lives thinking that cinema is reality, finally stand up and discover that movies are actually made by filmmakers who selectively display things for the entertainment and control of the masses.
In step two, an individual is dragged up a “rough, steep” path out of the cave and into the light. There, after acclimatization, that individual can see the eternal and unchanging ideas or forms that govern life in that cave. In this second step, the central idea (and hardest to grasp) is the Good, which Socrates compares to the Sun insofar as the Good illuminates and nurtures everything else. Later in The Republic, Socrates illustrates the relation between the ideas seen in the second step and particular examples by pointing out that while there are many beds there is a single concept “bed”, and knowledge involves grasping the concept in the examples.
But the bed example is just a teaching analogy. The ideas that occupy Socrates all have to do with human life, such as justice, truth, knowledge, love and courage. These ideas cannot be disproven or altered but are always at work, however dimly and inadequately, in cave activity. Understanding them is not becoming knowledgeable about, say, cosmology but becoming wise through a process of self-transformation in which one becomes able to be governed by the Good.
Remember it’s only an allegory: Socrates is playing a teacher’s role in trying to motivate Athenian youths, and the story aims to entice them to make the difficult journey up that rugged path. No deep reading is required to see that, in practice, education is a lifelong and never complete process. Thanks to our bodies and our mortality, humans never make it entirely out of the cave, which is their permanent home. Furthermore, there’s a third step in which the educated person, who is aware of the ideas, does not remain contemplating them, but attempts to use the acquired wisdom to interact with the other cave dwellers by returning into the cave.
And there’s another thing too: while the allegory is about education, Plato clearly means it to highlight the obstacles to education as well. One comes from an obsession with spectacle (think of the Internet and social media), which blocks the search for deeper truth. Another comes from powerful individuals who feel threatened by education and expertise, and try to quash them.
My problem with Rovelli and Krauss is their claim that science is the only mechanism to escape the cave and fulfill the educational process described by Socrates. This promotes a distorted and dangerous view of education. It bleaches from the realm of underlying reality anything that has to do with human existence. Socrates was interested in answering the question, “How should we human beings live?” and such an interpretation erases everything he cared about.
The critical point
In the cave, human beings have many different ways of living in which they seek love, prestige, pleasure, friendship, happiness and other kinds of “good” things, and the humanities seek to foster the wisdom that enables living well. Explaining the physical world – producing “effective images” of it – is only one of these ways. While the resulting images may help with other ways of living, they do not supplant them. To suggest that the scientific method replaces other ways of thinking and is the sole way to uncover underlying realities of the world not only fails to understand the cave allegory but also belittles the values and practices of the humanities.
These values include not only understanding ideas like justice but also things like Plato’s cave allegory. Calling science the way to escape Plato’s cave is an invalid interpretation – a dangerous one that attacks the humanities and wisdom they seek to foster. That, to me, is the most extreme hazard.
Volcanoes are intractable, majestic and enigmatic and there is something both primal and terrifying about watching them erupt, even at a safe distance. The juxtaposition of beauty and danger is a heady mix and many people, tourists and scientists alike, are drawn, inexorably, towards them. With that powerful attraction, however, comes risk.
Take the Volcán de Fuego in Guatemala, which rises sharply out of a gently sloping terrain of rich, lush volcanic soil covered in sugar-cane fields. It is an active volcano that has erupted violently more than 30 times in the last two years, and from the observatory where I’m staying, new sunlight bathes its peak, while the steaming plume emanating from the summit appears to glow.
Insects buzz, and students rustle in their sleeping bags as the first light catches their tents. The smell of coffee, good coffee, pervades the air. As a tractor, laden with cane farmers, chugs slowly past, it is impossible not to feel inspired by the backdrop. I know their day will be tougher than mine, but I retreat in solace to thinking about how our research should make them safer.
Deadly location
I am in Guatemala with a group of other volcanologists and engineers from the UK, and we are here to work with local scientists to investigate the volcano’s current activity and to examine how emissions from it affect the local population. It’s vital work because if Fuego erupted as strongly as it did in October 1974, the blast would devastate Guatemala and its people, more than 100,000 of whom now live within 10 km of the summit.
Among the dangers are the deadly avalanches of hot gas and rock that occur with alarming regularity. Indeed, these “pyroclastic density currents” (PDCs) are the biggest killers from volcanoes. Then there are the large mudslides that cascade down Fuego’s flanks every rainy season. Finally, there is the fine ash, which is produced whenever the volcano erupts and carpets the entire area, including local villages. Although it’s responsible for the wonderfully fertile local soil, the ash risks the health of those who breathe it in.
There is a lot we still need to know about the volcano’s activity and its hazards. In particular, we want to learn how to predict when the next eruption will occur and which valley any lava and PDCs will flow down. Our aim in regularly monitoring Fuego is therefore to get a better understanding of the volcano so that local people can take the best possible decisions next time it erupts. Unfortunately though, our task is not as simple as it sounds.
The summit of the Fuego volcano is inaccessible; it’s just too dangerous to get to the very top. You can’t get closer than 1 km from the peak and the nearest villages lie about 6 km away. This year we’ve therefore come armed with three different types of drone – or unmanned aerial vehicle (UAV), to use the jargon. It’s not the first time people have flown drones over volcanoes, but ours are geared more for research. So far we’ve used off-the-shelf cameras that can collect live data but we’re also developing different types of more specialized cameras to capture information.
During our first drone mission, we get a good view of the summit crater. Gustavo Chigna, Guatemala’s leading volcanologist and my collaborator for nearly 20 years, smiles broadly. He tells us it’s the first time he’s seen the summit in five years, the previous occasion being with a fixed-wing plane. The beauty of drones is that they give volcanologists a new, low-risk way of accessing volcanoes. Indeed, we’re moving beyond simply observing volcanoes with drones and starting to carry out proper, scientific measurements.
Fuego is an incredibly dynamic volcanic system. Its topography changes on timescales so rapid they feel alien to the two geologists on our team. Outcrops – exposed deposits from previous eruptions – are transient, sometimes vanishing in a single rainy season. As for the seven or eight valleys carved into Fuego’s side, they are constantly being filled by PDCs and eroded by mudslides. If a valley is full of material, the next flow might instead pour down the mountainside, which means that the valley and the local gradient of Fuego dictate the exact nature of any hazardous flows .
One project we’ve been working on is to create a detailed 3D topographical map of Fuego, which we would use to calculate how material flows down the sides of the mountain when it erupts. Unfortunately, an individual 2D image taken by a drone is not enough on its own. Using it to work out how lava flows down the mountain would be like pouring a cup of coffee on a flat photograph rather than over a papier-mâché model of the volcano. We therefore take many images of Fuego from about 60 different viewpoints and combine them using an off-the-shelf software package, such as Agisoft, in a process called structure from motion (SfM).
To do this, we need to know the precise location of the drone each time it captures an image, which we obtain using GPS trackers attached to the drone. The resulting map, or topographic digital elevation model (DEM), can be created in a few hours while we’re out in the field and consists of an array of numbers each of which corresponds to an elevation at a particular point on the volcano. Thanks to close-up pictures of the volcano taken by the drone (figure 1), each map has a resolution of a few centimetres, which is far better than the 30 m value from commercial DEM packages.
1 Close-up view A small ash explosion from the Fuego volcano, captured by a Phantom 3 drone. (Courtesy: University of Bristol, Cambridge & INSIVUMEH)
In practice, it is not easy to map those parts of the volcano where the drone images have low contrast (such as older lava flows), contain transparent bits (such as the plume), or have few features present. However, we can calculate the topography of valleys quickly and easily as they have good contrast and we’re mapping something solid, rather than a fluid-like plume. This work raises the tantalizing possibility of one day being able to map valleys in real time and so produce much more accurate predictions of where and how far material will flow. Our work is revolutionizing hazard prediction from volcanogenic flows.
Analysing the ash
Volcanologists don’t just rely on optical measurements, however. Ground-based cameras and satellite sensors can yield information about volcanoes at ultraviolet and infrared wavelengths too. So by using drones, we now have another way of studying volcanoes using these radiation bands.
Infrared light is particularly valuable as we can use it to calculate the heat flux from a volcano, to map and model the flow of lava, and to determine the composition of the lava from the precise frequencies the volcano emits. We can also use this infrared light to measure the amount of ash, carbon dioxide, sulphur dioxide and other gases, by working out how strongly they scatter and absorb thermal infrared light. Indeed, the beauty of using drones is that they give us a way of verifying satellite measurements of the amount of ash emitted by volcanoes. Whether the drones match the satellite data or tell a different story, however, is something we can’t yet tell.
The other important aspect of observations of volcanic emissions is that they are a proxy for what’s happening out of view. For example, in a volcano with an open vent that is producing sulphur dioxide, any jump in the rate of emission tends to signify that the volcano is about to erupt. Conversely, if the vent closes up, any drop in emissions could mean pressure is building up and the volcano is about to explode.
We shouldn’t forget either that volcanic emissions are dangerous. Gases such as sulphur dioxide are toxic to humans, plants and animals, while the ash particles, if small enough, can cause cancer. And if the ash ends up in the engine of an aeroplane that happens to be flying by, it can damage the turbine and, in extreme cases, cause it to cut out entirely. Rain can also turn ash into catastrophic mudslides, potentially sending it tens of kilometres further afield, creating a secondary hazard to people living relatively far from the volcano. Estimates suggest there’s enough ash on the flanks of Fuego to generate mudslides for the next 20 years, even if the volcano never erupts during that time.
Unfortunately, there are big uncertainties when using infrared observations to determine the size distribution of volcanic ash particles as we have only a handful of wavelength bands at our disposal. These particle-size distributions are important as they are largely responsible for dictating the fate of an ash cloud and are an important parameter in models that predict where ash goes in the atmosphere after an eruption. In fact, until recently, volcanologists relied on a particle-size distribution in the range 1–100 µm that had been measured in 1989 by Peter Hobbs, an atmospheric scientist from the University of Washington in the US, which was used to manage large swathes of global airspace. The problem is that this single distribution is unlikely to be characteristic of all ejected volcanic ash, which depends a lot on the amount and crystalline structure of silica in a volcano, as well as on how it erupts.
Another key aim of our project at Fuego has therefore been to capture and examine volcanic ash in situ using drones. It’s been done before using balloons flying over a number of volcanoes in places such as Costa Rica and Indonesia, but those missions have only been at high altitude – typically about 10 km up. That makes it tricky to control a balloon so that it flies where you want it to go; although it will fly rapidly through a plume in a horizontal direction, if you happen to miss the plume, you can’t redirect the balloon.
During our last trip the engineers on our team managed to get a drone known as a “quadcopter” close enough to make observations of Fuego’s vent and of the plume of gas from a second volcano, Pacaya. We also flew a fixed-wing aircraft through Fuego’s ash clouds for the first time.
The future’s up in the air
Drones are giving volcanologists unprecedented access to – and high-quality data for – areas that were unthinkable even a decade ago. My prediction is that it will become routine to use drones to monitor volcanoes over the next few decades – all we need is for physicists, engineers and geologists to continue working together. In the short term, my colleagues and I are all heading back to Guatemala later this autumn to continue our effort. We’re all excited by the prospect, and can’t wait to get back into the air.
How to study volcanoes with drones
Inside information: the author and colleagues are mapping and monitoring Volcán de Fuego using unmanned aircraft. (Courtesy: Matthew Watson)
The engineers on the UK team studying the Volcán de Fuego in Guatemala have trialled three systems for flying over this dangerous volcano, all of which are powered by electric engines. The first is an off-the-shelf DJI Phantom 3 Pro quadcopter with a standard 4K camera (bottom right in photo). This drone has let us create 3D maps, known as digital elevation models, of both the summit crater and the valleys down which hazardous material travels. These models have, in turn, helped us make predictions about the timing and direction of the next eruption and what materials it might contain. To this system we’ve also added an infrared camera from the US firm Therm-App, which we’ve used to survey lava flows. Unfortunately, we can’t add any more kit as the quadcopter’s maximum payload is only 300 g.
The second system we’ve used is a Ritewing Zephyr 2 delta-wing aircraft (bottom left in photo), which has a wingspan of 1.5 m and can carry a payload of 800 g. We have used it to collect ash samples from the volcano by sticking adhesive tape on its leading edges and installing a filter pack with pump on the front. The craft also has a series of lightweight sensors that monitor air pressure, temperature and relative humidity. The beauty of this system is that because the ash sensors are on the front but the craft is powered by a rear-mounted propeller, we reduce the number of fine particles lost from air disturbance.
Our final system for studying the Volcán de Fuego is a small glider known as a Thermik XXXL (rear of photo). Launched using a catapult, it has a 5 m wingspan and can carry a 1.1 kg scientific payload. Although this craft has a front-mounted propeller, it can be folded backwards in flight so the aircraft glides through the plume. We’ve already trialled the glider and our plan now is to fit it with both gas and ash sensors, along with a pointable infrared camera.
Despite more than 30 years of campaigning by learned societies and community interest groups, the statistics for women in science are grim. In the UK, girls make up one-fifth of A-level physics classes and only 9% of professional engineers. Although it has become trendy to talk about diversity, to offer “women in science” scholarships and to decorate laboratory walls with photographs of women in lab coats, there are still external forces at play that prevent women from being as successful in science as their male counterparts. In Inferior: How Science Got Women Wrong and the New Research That’s Rewriting the Story, author Angela Saini puts forward the idea that bad science has been used to endorse the cultural prejudice that women are both biologically and psychologically second rate to men.
The book contains an impressive collection of studies spanning psychology, biology and neuroscience, which highlight misconceptions – such as claims that women are “better at multi-tasking” or “don’t like playing chess” – that have become ingrained into our society, but have no scientific basis. An engineer by training, Saini makes complicated studies accessible for non-specialists: studying humans is a completely different discipline from most physics research. The language is clear and non-judgemental and Saini makes her case with meticulous detail, taking care to remain non-biased throughout. Inferior is not a collection of complaints about the lack of women in science. Instead, it is an objective critical analysis into what research has overlooked.
This is an admirable mission. Throughout the book Saini travels long distances only to interview people who seem to have made it their life’s work to prove women are weaker than men. For example, Saini was at an event promoting her previous book Geek Nation when she was approached by an audience member who made derogatory comments about women’s academic achievement. This is one of very few personal anecdotes in the book and serves to remind the reader of the need for this kind of work.
It was only in 1993 that it became a requirement to involve women as subjects in medical trials. It is well documented that women live longer and are more resilient to certain diseases, but there has been little biological investigation as to why. We are introduced to the gender studies of Simon Baron-Cohen – a professor of developmental psychopathy at the University of Cambridge, who has spent years trying to find differences between the brains of men and women – that are now open to serious questioning. Saini’s wit makes even the most depressing studies light and easy to read. In his own book The Essential Difference, Baron-Cohen’s description of the hobbies of those with a “male brain” (DIY, programming, tweaking sound systems) are lazy and dated, and Saini points out they are also painfully middle class and English.
Saini describes that something as simple as a misworded press release with a flashy headline can be reproduced in national newspapers, and our interpretation of such information is usually shaped by any prejudices we already have. Inferior transitions seamlessly from the human to the animal kingdom, where we have chosen to extend our human stereotypes. She visits zoos, observes animals and talks to experts. The public are likely to be familiar with the well-documented studies of controlling male baboons and hierarchical male chimpanzees; whereas we rarely read of the aggressive female bonobos or promiscuous bluebirds. She points out that if brain size is linked to intelligence, we’d expect blue whales to outwit us all.
There are an estimated 100 trillion synapses in the human brain – 1000 times more than the number of stars in the galaxy. The invention of functional magnetic resonance imaging (f-MRI), which maps brain activity, allows us to identify parts of the brain associated with specific tasks. Simple and seductive, neuroscience offered the promise of understanding everything from emotions to addiction. f-MRI became the 1990s go-to technique for characterizing gender differences. But the statistics were sloppy, and bold claims made using small sample sizes, combined with questionable peer review, led to results that could not be reproduced. In 2009 in a lab at Dartmouth College in the US, neuroscientist Craig Bennett famously recorded brain activity in a dead Atlantic salmon. His study demonstrated the dangers of statistical errors in f-MRI.
The book began as an investigation into the science behind menopause. Until the late 1930s it was regarded as a disease – one that drove women mad. Treatments were, at worst, lethal and varied from being sent to an insane asylum to poison. Once endocrinology had revealed the hormonal changes behind menopause, scientists tried to fix it. By the 1960s American drug companies were selling hormone-replacement therapy as an anti-ageing elixir. The “youth-restoring blend of oestrogen” promised to keep women attractive and interesting. In the 1990s dangerous links between oestrogen-replacement therapy and cancer were found, not to mention an increased risk of heart attack and stroke. Today, hormone-replacement therapies are much more regulated and prescribed only for short periods of time – and the medical jury is still out on just how safe and effective they are. Male academics still claim that menopause is nature’s way of saying older women aren’t sexually attractive. Through discussion with acclaimed primatologist Sarah Hrdy at the University of California at Davis in the US, Saini demonstrates that menopausal women are far from useless. The “grandmother hypothesis” describes how older women who look after the second generation enhance social networks and ensure genetic survival.
Inferior is an engaging and harrowing study that easily moves between eras, continents and disciplines. Saini is a meticulous researcher whose attention to detail is evident in her interviews with scientists behind some of the biggest results in neuroscience and psychology. Instead of writing around the issue of representation of women in science, Saini identifies what science has got wrong about women. Her research demonstrates it is the scientists themselves who are partly to blame, peppered with in-built prejudice from centuries of cultural conditioning. It is my hope that this important book encourages scientists and educationists of the need for more evidence-based approaches to ensure equality and diversity in science.
Working near each other can boost collaboration among researchers, according to a team at Massachusetts Institute of Technology (MIT) in the US. Matthew Claudel and colleagues examined the relationship between researchers’ collaborations and their physical proximity with each other around the MIT campus.
By analysing 40,358 papers and 2350 patents covering MIT research between 2004 and 2014, they found that spatial relationship was more important than departmental and institutional structures. “Intuitively, there is a connection between space and collaboration,” says Matthew Claudel. “That is, you have a better chance of meeting someone, connecting, and working together if you are close by spatially.”
Campus-wide study
The study confirms and extends the Allen Curve – a theory by Thomas Allen in the 1970s that proposed collaboration and interaction decrease as a function of distance. Allen even found that basic conversations were less like to occur when people were 10 m apart. Rather than just focusing on a single building as Allen did, the current work looked at campus-wide collaboration and interdisciplinary research across 33 MIT departments and programmes.
The team found that collaboration on patents has a slightly different dependence on distance than papers. Researchers in the same workspace are more than twice as likely to work together on both papers and patents than those 400 m apart. For papers the likelihood drops by a half when researchers are separated by 800 m, but for patents it drops in half less steeply, over 1600 m.
Importance of architecture
The paper, published in PLOS ONE, also discusses the importance of architecture on interdisciplinary research. The MIT buildings with the most collaboration were specifically designed to house a diverse set of researchers. For example, the Koch Institute for Integrative Cancer Research – which had the highest rate of co-authorship – was specifically designed to mix research scientists and bioengineering experts so as to encourage novel cancer-fighting technology. “If you work near someone, you’re more likely to have substantive conversations more frequently,” says Claudel.
One for the future Condensed-matter physicist Xinzheng Li from Peking University. (Courtesy: Xinzheng Li)
What research does your group carry out?
Since 2012 I have led the path-integral group in the Institute of Condensed Matter and Materials Physics at Peking University (PKU). We have around seven people in the group. Our research lies between traditional condensed-matter physics and chemical physics. We focus mainly on the development of computer-simulation methods and their applications to molecular and condensed-matter systems.
What specific systems are you studying?
We use path-integral molecular dynamics to study the influence of nuclear quantum effects on the properties of molecules
and condensed-matter systems. We recently discovered a low-temperature metallic liquid state of hydrogen at high pressure (Nature Comms4 2064) and also study the quantum nature of hydrogen bonds (Science352 321). More recently, we have been working on phase transitions between paraelectric and ferroelectric states and the existence of quantum paraelectricity.
Do you collaborate with other groups in China?
We work with an experimental group at PKU that undertakes low-temperature scanning tunnelling microscopy imaging.
What about further afield?
We have intensive collaborations with universities outside of China, for example University College London and the University of Cambridge in the UK. Maintaining such collaborations is crucial in keeping my own research in China to a good standard.
Why did you go to Europe early in your career?
I completed my Master’s degree in physics in 2003 at the Institute of Semiconductors, Chinese Academy of Sciences. I initially planned to go to the US for my PhD, but student visas were restricted following the terrorist attack on New York in September 2001. I then applied to the group of Matthias Scheffler at the Fritz-Haber Institute of the Max-Planck Society in Berlin, who offered me a PhD position. When I look back on this experience at one of the top research groups in my area, I am extremely pleased that I went to his group.
Was it unusual at the time for Chinese students to go abroad?
For Chinese scientists of my generation, getting good training in Europe or US is a very natural choice. Personally, I really wanted to learn something new so that when I finished my studies and eventually came back to China I could carry out decent research of my own.
What did you do after your PhD?
From 2008 to 2011 I did a postdoc at University College London where I learned how to carry out independent research.
How did your time in Europe affect you?
My time in Germany and the UK basically defined me as a scientist.
Why did you come back to China?
There are much better funding programmes in China for young researchers and this is very important if you want to have an academic career. The 1000 Talents programme is well known for successfully attracting young researchers to come back. In addition to this – and even more important – the National Natural Science Foundation is very supportive to young researchers. All of this together can help one get a good start in their research career.
How would you compare the research culture between the West and China?
Research in China is much more influenced by what is carried out in the US than, say, Europe. At least this is how I feel as a young researcher. In Europe, people can work on one specific topic for years without being pressured to publish in high-impact journals. So, for example, they can work on different computer-simulation methods without the need to deliver immediate results.
How can China learn from this?
We do need to learn. But one advantage we have is that the funding system is very generous and I hope that continues. If it does, we really need to make good use of such an opportunity to catch up.
How has your research experience influenced how you recruit your own research team?
My independent academic career started five years ago and since then I have recruited one postdoc and some PhD students, who are all from China. I strongly recommend them to go to Europe or US for further training. I also hope that I can recruit some members outside of China in the future.
What challenges are there in recruiting people from outside China?
The challenges include facing up to what is the traditional pattern for having a successful academic career. For people who want to work or study in China, but eventually go back to their own countries for a permanent job, the experience in China may not help them that much. In recent years, I see some change in that there are more students or postdocs coming to China, but the number is low. For them, it may take a longer time to create an academic reputation.
The guide hall at the HANARO research reactor in Daejeon, Republic of Korea.
By Margaret Harris in Daejeon, Republic of Korea
For almost three years, the HANARO research reactor has been idle. Built in 1995 as a hub for neutron-scattering experiments, radioisotope production and other scientific work, HANARO (High Flux Advanced Neutron Application Reactor) is the only facility of its kind in the Republic of Korea, and it underwent a major upgrade in 2009. Then, in 2014, the facility became a delayed casualty of the meltdown at Japan’s Fukushima Dai-Ichi nuclear power station, as enhanced regulatory scrutiny led to the discovery that the reactor hall’s outer wall was not up to the latest standards. An enforced shutdown followed while the wall was reinforced, and although the works were supposed to take just 18 months, opposition from local citizens’ groups has led to further delays.
Physicists at the University of Kaiserslautern in Germany have observed how individual atoms diffuse through a gas for the first time, and how individual collisions between particles affect diffusion. The new study could help model diffusion in rarefied environments, such as thin layers of air in the upper atmosphere, in interstellar space or in vacuum systems.
Diffusion is the process whereby tiny particles uniformly disperse throughout a gas or liquid. Although these media are made up of individual particles, researchers usually describe diffusion as a continuous process.
Diffusion was first described by the Scottish botanist Robert Brown, who observed that grains of pollen appear to quiver as they zigzag through a liquid. This movement came to be known as Brownian motion and it allows substances to disperse and mix. Albert Einstein, in his seminal 1905 paper, explained diffusion at the microscopic level and showed that Brownian motion comes about thanks to collisions of particles with molecules of the surrounding medium.
Billions of collisions
In early studies of Brownian motion, the particles considered were much larger than the molecules in the medium. This means that billions of collisions are required to change the path of such particles. Not every collision is tracked in such studies. Rather, the collective effects of impacts are modelled as a randomly fluctuating process. When combined with the medium’s viscosity, the particle’s energy loss to its surroundings can be calculated. This approach is described by the Langevin equation, which can be used to calculate, for example, how a particle’s average speed changes over time.
However, individual collisions are much more important when the particles have roughly the same mass as the atoms of the gas or liquid medium. To study this scenario, a team led by Artur Widera looked at how a few caesium atoms diffuse through a thin cloud of ultracold rubidium atoms held within an optical trap. Operating at a very low temperature drastically reduces collisions between the caesium and rubidium atoms so that their individual motions can be observed.
The experiment involves firing caesium atoms one by one into the gas. After a certain time delay the team froze the motion of the caesium atoms by applying a light field to the trap and recorded the positions of the trapped atoms using a different laser beam.
Nearly thermalized
By varying the delay between when the caesium atoms are introduced and when they are frozen, the researchers were able to determine how the motions of the caesium atoms change when they collide with the rubidium atoms. They showed that just one collision can strip enough kinetic energy from a caesium atom so that it ends up with almost the same energy as the surrounding rubidium atoms. The caesium atom is thus nearly in thermal equilibrium with the surrounding rubidium atoms after one collision.
Although far from the classical situation in which the Langevin equation applies, Widera’s team discovered that the equation can work under these experimental conditions. However, the equation must first be modified to include a friction coefficient that describes how the viscosity of the medium depends on the velocity of the diffusing atoms.
This modified Langevin equation could be used to describe diffusion that does not involve a continuous medium, say the researchers. Examples are aerosols (mixtures of suspended particles) dispersed in thin layers of air in the upper atmosphere, in interstellar space or in vacuum systems.
Almost 10% of people working in US astronomy have suffered from physical harassment at work, according to a survey carried out by researchers in the US. Led by Kathryn Clancy, a social scientist from the University of Illinois at Urbana-Champaign, the survey asked 423 students, academics and administrators 39 questions about their working environment.
Around 88% of respondents reported hearing, experiencing or witnessing negative language or harassment that was related to race or gender. The survey also found that 39% of respondents were verbally harassed and that 40% of non-white female respondents said that they felt unsafe at work as a result of their race and gender.
Clancy’s co-authors on the study are Illinois social scientist Katherine Lee, astrophysicist Erica Rodgers of the Space Science Institute in Colorado, and Christina Richey, who is a planetary scientist at the American Astronomical Society.
Physicists in China have achieved the first quantum teleportation from Earth to a satellite, while their counterparts in Japan are the first to use a microsatellite for quantum communications. Both achievements suggest that practical satellite-based quantum communications could soon be a reality.
Jian-Wei Pan of the University of Science and Technology of China in Hefei and colleagues used China’s $100m Quantum Experiments at Space Scale (QUESS) satellite to receive a quantum-teleported state. This was done over a distance of 1400 km from a high-altitude (5100 m) ground station in Tibet to QUESS. This is more than 10 times further than the 100 km or so possible by sending photons through optical fibres or through free space between ground-based stations.
Meanwhile, Masahide Sasaki and colleagues at the National Institute of Information and Communications Technology in Japan have shown that quantum information can be transmitted to Earth from a 5.9 kg photon source called SOTA – which is on board a 48 kg Japanese microsatellite called SOCRATES.
Quantum key distribution
Writing in Nature Photonics, Sasaki’s team reports that they were able to receive and process the information at a ground station in Japan using a quantum key distribution (QKD) protocol. QKD uses principles of quantum mechanics to ensure that two parties can share an encryption key secure in the knowledge that it has not been intercepted by a third party.
